Uefa launched an investigation last night into allegations that Patrick Vieira was racially abused by Lazio's Sinisa Mihajlovic throughout Arsenal's Champions League game in Rome.

Vieira has claimed the abuse heaped on him by the Yugoslavia defender was the worst he had heard.

The behaviour of Lazio fans, who taunted Arsenal's black players and hurled objects at the team at the end of Tuesday's 1-1 draw, will also be investigated.

"Mihajlovic called me a fucking black monkey and when you are a player you are not happy to hear that," said Vieira, who in the past might easily have lost his cool in the face of such provocation. "What is really surprising is it has come from a player who is a foreigner in Italy.

"It started in the first game at Highbury and I thought maybe it was just because we won the game that he was upset. When a fan does it it's stupid, when a player does it it's unbelievable. It is the worst abuse I have ever heard and it never stopped from the moment the teams were shaking hands at the start. I told him he'd said enough.

"You could see in his eyes that he was really thinking about what he said. It was very hurtful and difficult to accept when another pro player says things like that.

"When fans do it, you can do something about it; they can be identified. But when a player says it to you on the pitch it is difficult to prove. I feel I have to speak out about this and do something. You have to tell the truth."

Mihajlovic admitted last night he had made reference to Vieira's colour but denied the insults were racist and claimed Vieira had started the squabble by calling him a gypsy. "Yes, it's true I said 'black shit', but he provoked me by saying 'gypsy shit'," he said. "I called him black but I might just as well have called him French. If I'm a racist then at this point so is he for calling me a gypsy.

"I don't have anything against blacks. I didn't want to insult him because of the colour of his skin, just as I'm sure he didn't want to insult me by calling me gypsy."

Depending on what is included in the report filed by the German referee Helmut Krug, and possible evidence presented by other independent witnesses, Uefa may have trouble making charges stick against Mihajlovic.

But Lazio face a fine at the very least. Uefa recently fined Red Star Belgrade £16,000 after their fans hurled flares at Leicester supporters and shouted racist abuse.

"Uefa absolutely condemns all forms of racist abuse," said its director of communications Mike Lee. "When any allegation of this kind is made we take it extremely seriously."

Lazio are known for attracting an extreme right-wing fringe and their president Sergio Cragnotti has apologised for Tuesday's racist behaviour of a section of fans. But Lazio insisted the abuse was the work of "a few hundred imbeciles" and hit out at a "defamatory campaign" to brand the club and its supporters as racist.

Having received the reports of Krug and its match delegate, Uefa is also investigating the ill-tempered squabbles that marred the evening. They included Arsenal's Gilles Grimandi striking Diego Simeone, leaving the midfielder with a cut above his eye, and an after-match fight involving Grimandi, Mihajlovic and his Lazio team-mate Alessandro Nesta.

Grimandi, who said he pushed Simeone away after having his shirt tugged but did not punch him or try to hurt him, can expect a suspension.

Mihajlovic claimed the Arsenal vice-chairman David Dein was "involved in the uproar at the end", but that was denied by Dein.

 Rome prosecutors have asked for Lazio's president Sergio Cragnotti and Juan Veron to be indicted over alleged document-faking to get the Argentine an Italian passport. It is claimed that Veron's dual citizenship helped Lazio field an extra, prohibited non-European Union player in some games last season.